At the present time lumbar disc herniations with neural compression are almost always operated on from a posterior approach (from behind). Once the disc herniation is surgically exposed the disc itself is generally entered either through a pre-existent hole in the annulus (fibrosis casing of the disc), or an opening is made with a knife. Various instruments are then utilized to either scrape the disc material from between the vertebrae, e.g. currettes; or to bite it, e.g. rongeurs. Because of the presence of the relatively fixed dural sac and the nerve roots which are only minimally mobilizable, the access opening is relatively small in relation to the volume of the disc. During this procedure, the goal is to remove not the entire disc but rather that portion which is at risk to fragment off or reherniate.
Generally, at the completion of the procedure there is a small access window into the disc, lateral to the dural sac and traversing nerve root but medial to the exiting nerve root, and a relatively large disc space, corresponding to the removed portion of the disc, surrounded by the otherwise intact annulus fibrosis and all of the residual nucleus, which is usually rather considerable. Because of the relatively large excavation in relation to the small access opening, it is generally not possible to visualize the entire disc space. Therefore, it is possible for disc fragments to be free in the disc space or to be partially free and only tenuously attached. If not removed, such fragments could, after the surgery, extrude into the spinal canal and either compress or inflame the neural elements, or both, resulting in the failure of the original surgery and resulting in the need for an additional surgery to correct the condition. Such postoperative disc surgeries are quite common and probably occur with a frequency of ten to twenty percent. As is it is not unusual for these patients to at first have experienced relief of all leg pain and then to shortly after being mobilized to have the reherniation, it is generally believed that the residual freed, but not removed, or nearly free fragments are forcefully extruded from the disc space when the disc space is significantly compressed from the patient assuming the seated or standing positions.
At present, therefore, in an attempt to remove such disc fragments during the original surgery and to avoid the above described problems, it is the accepted and customary practice to attempt to irrigate, or wash out, the disc space after the completion of the partial disc removal procedure. Three means are currently used to perform such an irrigation. First, one can take an irrigation bulb (see FIG. 1) and aim it at the disc opening so that as much of the stream of fluid as possible goes into the disc space. Secondly, one can take an ordinary syringe and again aim the stream at the disc opening. Thirdly, one can place the end of a catheter (a small hose) into the disc space itself and then irrigate the space through that small tube.
The first and second above methods are only minimally effective in that the tip of the irrigation source is quite some distance from the opening itself, and even when some portion of the stream passes through the disc opening, the path is determined by the relatively fixed location of the opening and the tip such that the disc space is not effectively irrigated. The third method, while delivering the fluid within the disc space, is also less than optimally effective as it is difficult to direct the tip in a global fashion as would be needed. Also, since it is lacking some means of occluding the entrance to the space, the fluid tends to simply run out of the access opening rather than mobilize the debris fragments.
Unfortunately, to whatever degree the above methods are effective, they are also quite dangerous. Since the opening to the disc space is not occluded during the irrigation process, any fragments successfully mobilized are blown into the spinal canal above, beside, or under the dural sac and nerve roots. If the fragments irrigated from the disc space come to lie beneath the neural elements the surgery may result in a failure. Alternatively, a fragment may follow the path of least resistance and be washed out along the path of the nerve as it exits the spinal canal in the area called the neural foramen. However, there may be insufficient fluid pressure to cause the fragment to exit and the fragment may then plug the passageway compressing the nerve root. Alternatively, as shown in FIG. 2 the fragment may not even make it quite that far and may become trapped by the filmy tissue about the nerve root anywhere within that passageway resulting in a source of irritation to the nerve.
Aware of these undesirable possibilities, it is a common practice following the irrigation of the interspace by one of the known means, as shown in FIG. 3, to then take a 90 degree (right angle) probe and to attempt to blindly feel about beneath the dural sac and nerve roots in the hope of hooking any extruded fragments. While this is sometimes successful, it may instead result in the hidden fragments being actually blindly pushed further beneath the neural structures, thus making these fragments less retrievable and increasing the severity of the neural compression. Furthermore, attempts at blindly sweeping the spinal canal floor are usually met by the disruption of the extremely fragile epidural veins which are a potential source of significant blood loss and later dural compression by the resultant hematomas. Control of the bleeding by electrocoagulation is rarely possible as these vessel ruptures are not accessible, having occurred in the blind area beneath the neural elements or out in the foramen.
In summary then, at present there is clearly a need for a safe and effective means of irrigating the disc space following discectomy.